On Apr 23, 2014 10:28 PM, "Rick - DJ0IP / NJ0IP" <Rick@dj0ip.de> wrote:
>
> Lee,
>
> I think it is impossible for anyone to predict what is going to happen
when
> using an indoor antenna.
> I don't expect the Jupiter to work better than the Kenwood in combating
> those specific problems, but the Jupiter is a fine radio.
>
> You have three problems you're fighting:
>
> 1) Very weak "wanted signal" compared to when using an outdoor antenna
> 2) The garbage being picked up by the antenna inside the house from
consumer
> products
> 3) Common Mode Current (CMC) from the antenna radiating into its own coax
> line, which is what is making the transceiver go crazy.
>
> There is no silver bullet for #1. By far and away the best thing I have
> ever used indoors is a magnetic loop antenna. I have even used one out of
> the basement of a hotel and still worked all over Europe with it
Do you think a mag loop would have any gain over the hamstick dipole I use
now?
I feel I actually put out a halfway decent signal. The problems is hearing
anything over that clamor.
I've heard about some receiving antennas in a loop configuration that
actually do very well and are quite small; however they require a decent
preamp.
(BTW - I'm
> in Europe, so that was not DX). If you can, run a nearly invisible wire
out
> into the yard to a tree. You can use thin copper enamel wire. Then remove
> it during the day. This will outperform anything you do indoors.
>
> The magnetic loop will also help a little with #2. For one thing you can
> rotate it, and sometimes that can help to reduce the level of disturbance
> from the consumer products, thus dropping your noise level a few S-Units.
>
> For #3 you definitely should buy or even better, build a good quality RF
> Choke and insert it in the coax line directly at the transceiver. Most
> people couldn't be bothered with taking the time to learn about good RF
> Chokes, and thus think any old thing they buy is going to be good.
Indeed,
> any old thing will help but in tough cases, you need a good choke, not
just
> any old choke.
>
> TWO KINDS of RF CHOKES: There is the Maxwell (W2DU) and the Guanella.
MOST
> commercial chokes are Maxwell and most people use this kind. This is the
> "ferrite beads over coax" type of choke. It often will suffice but in
tough
> cases, the Guanella is a lot better - with a caveat. The W2DU is more
> broad-banded; the Guanella is more frequency dependent but much better
over
> a limited frequency range. As a result, the Guanella will work much
better
> than the W2DU for several bands, but its suppression ability drops off
above
> and below these bands - however it still works as well as the W2DU outside
> of those bands. SOUNDS COMPLICATED - BUT'S ITS NOT. (I can help you if
you
> like.)
>
> For buying or building a W2DU, I would go to THE WIREMAN, model 8231 ($30)
> or the kit version of it, 8331 ($20).
> The model T4 or T4G from The Radio Works is just as good, but costs twice
as
> much and is big and bulky.
> I haven't tried the low power version of the Radio Works choke so I won't
> comment on it.
>
> There aren't many commercial Guanella chokes available and the ones that
> are, cost a lot of money.
> These are "simple Simon" to build. Simply wind a piece of coax around a
> toroid core and solder a PL-259 on each end.
> The questions of course are always "which core" and "how many turns of
> coax".
> Here too a simple solution exists: Steve, G3TXQ has an excellent web page
> with a lovely color (colour) chart showing which toroids and how many
turns
> of coax, frequency dependent.
> See: http://www.karinya.net/g3txq/chokes/
> IMO, STEVE'S PAGE IS ONE OF THE MOST VALUABLE PAGES ON THE INTERNET FOR US
> HAMS! TNX STEVE!
>
> Here is a picture showing how easy it is to home-brew:
> http://www.dj0ip.de/cmc-test/the-components/the-chokes/
> Look at the 3rd choke from the top, entitled "C3".
> From the larger picture in the clickable gallery, you will see that I
> cross-wound this choke.
> However that is not necessary. You can simply wind the coax in one
> direction, all the way around the toroid. The only advantage of
> cross-winding is that the two ends of the coax exit the toroid on opposite
> sides.
> I think this one cost me about $10 and it is SUPERIOR to the W2DU type
> chokes.
>
> If you want to buy a Guanella choke:
>
http://www.balundesigns.com/servlet/the-32/balun-designs-baluns-1-cln-1/Deta
> il
> ($65)
>
> UNFORTUNATELY I cannot guarantee that any of these will make a significant
> difference to the RX noise - there's a good chance they will help, but no
> guarantees.
> But they should fix the problem with the transmitter going crazy above
40w.
>
> Good luck, Lee!
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
Many thanks Rick. This is very useful to me, and I may implement one or
more of them as occassion requires.
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|